Apparatus and method for measuring and analyzing dynamic processes

ABSTRACT

Apparatus and method for analyzing dynamic processes represented by a particular time variable information signal within a range for amplitudes of the signal, wherein a signal analyzing amplitude band is defined and particular characteristic portions of the signal when occurring within the band are detected. By means of sweep signal the analyzing band is shifted across the amplitude range and the detected events are accumulated as statistical representation evaluation of the occurrence of the characteristic portions in dependence upon amplitude as represented by the sweep signal as defining the position of the analyzing band within the amplitude range.

Euer et al. 51 May 23, 1972 APPARATUS AND NIETHOD FOR e ences CitedMEASURING AND ANALYZING UMTED STATESPATENTS DYNAMIC PROCESSES 2,970,2611/1961 Zoll ..324/77 X [72] Inventors: l-lartmut Euer; Guenter Pauli,both of Mu- 3,122,732 2/1964 Lewinstein et al. ..324/77 X nich, Germany3,243,656 3/1966 Baude ..324/77 X [73] Assignee: \ferelnlgte Flugtechnlsche Werke Fokker Pn-mary Examiner Edward Kubasiewicz ('mbH, Bremen,Germany Attorney-Smyth, Roston & Pavitt 22 F1 d: A 22 1970 l 1 pr 7 57ABSTRACT [21] Appl' 30885 Apparatus and method for analyzing dynamicprocesses represented by a particular time variable information signal[30] Foreign A li ation P i it Dat within a range for amplitudes of thesignal, wherein a signal analyzing amplitude band is defined andparticular charac- Apr. 24, 1969 Germany ..P 19 20 964.4 teristicportions f the signal when occurring within the band are detected. Bymeans of sweep signal the analyzing band is [52] US. Cl. ..324/77 Ashifted across the amplitude range and the detected events are [51..G0lr 23/16, GOlr 27/02 accumulated as statistical representationevaluation of the oc- [58] Field of Search ..324/77 A currcnce of thecharacteristic portions in dependence upon amplitude as represented bythe sweep signal as defining the position of the analyzing band withinthe amplitude range.

16 Claims, 6 Drawing Figures zera O in/7y 0! e: a! 17 Var/mm +0 ffiefec/a/T 1! aye/ f 2 1 ew/m/ 1' /e Mia .1 5 I Amp f fi T i and z '7 7Fi/ler l/e/ivar l (mflgflf 45 I 0072, du/pzl/ l C Ol/S/lZ/zf 6 l enfiv93 a/ef 19 jman g Qwemmr T Kale 4 Confro/ v x fi/affer APPARATUS ANDMETHOD FOR MEASURING AND ANALYZING DYNAMIC PROCESSES The presentinvention relates to a method and apparatus for measuring and analyzingdynamic processes, wherein particularly the behavior of a physicalquantity in time is analyzed and processes by counting particular eventswhich occur in analyzing bands to obtain statistical, characteristicfunctions. The invention relates particularly to the statisticalanalyzation of signals seemingly having random behavior as a result ofsuperpositioning of different phenomena.

It is known to develop statistical characteristic function of any kindof dynamic process in that the behavior in time, i.e., the temporalcharacteristics of the respective physical quantity is investigated asto particular events within a particular range or continuum ofamplitudes. For this it'is customary to subdivide the analyzing range ofthe physical quantity into several analyzing bands which run in parallelto the time axis. The particular events of interest are countedindividually as they occur in the individual analyzing bands. Thismethod, however, has the disadvantage that the accuracy of the resultingcharacteristic function depends upon the number of analyzing bands thusdefined, i.e., the accuracy depends upon the resolution of subdivisionof the analyzing range. It is rather uneconomical to provide equipmentso as to subdivide the analyzing amplitude range in as many smallanalyzing bands as required for particular requirements as toresolution. As a consequence, the ascertained characteristic functionsinclude considerable errors.

The teaching of the invention has as its principal task to avoid thesedisadvantages. The disadvantages are avoided by providing an analyzingband which is variable in width (that is the dimension transverse to thetime axis), by causing the analyzing band to progressively sweep theanalyzing amplitude range, and by detecting the particularcharacteristic events as they fall into the band. The detected eventsare counted and the counting result is considered in relation to theamplitude value defining the current position of the analyzing bandwithin the amplitude range.

This method offers the possibility of ascertaining characteristicfunctions with comparatively little expenditure. For example, thedistribution and frequency of relative or absolute maxima or minima mayreadily be detected. Also, probability distribution and distributiondensity can readily be ascertained. The analyzing area may be sweeped byshifting the analyzing band across the amplitude range continously or infinite steps. In case of a stepwise sweeping of the amplitude range itis of advantage to match the width of the analyzing band with the widthof the step for shifting the analyzing band across the analyzing range.Also, the sweeping speed for the analyzing band can be varied withinselected limits and direction of sweeping may reversed.

While the specification concludes with claims particularly pointing outand distinctly claiming the subject matter which is regarded as theinvention, it is believed that the invention, the objects anf featuresof the invention and further objects, features and advantages thereofwill be better understood from the following description taken inconnection with the accompanying drawings in which:

FIG. 1 illustrates schematically a plot of a function representing aphysical quantity variable in time;

FIG. la illustrates a block diagram of an apparatus for practicing thepreferred embodiment of the invention; and

FIGS. 2 through 5 illustrate plots identifying particular events to bedetected for statistical evaluation.

Proceeding now to a detailed description of the drawings, in FIG. 1thereof a curve has been plotted representing, for example, theinstantaneous magnitude of a physical quantity, for example theamplitude of a particular event as it varies in time and beingrepresented by a function X of time t. The curve to be analyzed, may,for example, represent a frequency distribution resulting frominvestigating the strength of materia]; or the curve may represent acomposite signal, such as an acoustic signal or the like with seeminglyrandom distribution of signal peaks of different amplitude, and theamplitude distribution is to be ascertained and statistically evaluated.

The double arrow 12 denotes the total amplitude range in which amplitudevalues of the curve 10 are expected to be found; it is basically assumedthat function X (I), as representing the phenomenon to be investigated,has a range for amplitude values which, for example, for principlereasons, will not exceed that amplitude range. For example, that range12 may be defined by maximum response limit of measuring transducers. Orin case, the curve represents an attenuated output, the range 12 isdefined by the input, and the attenuation is the subject of theinvestigation.

In the general case an analyzing area or range 11 may be defined within,for example, the theoretical amplitude range 12, which range 11 may beequal to the total amplitude range but may be smaller due to additional,for example, practical restrictions on the representation of thequantity as represented by the curve. The analyzing area 11, as plottedin FIG. 1, therefore, is expected to cover a smaller amplitude rangethan range 12. The size of the analyzing range 11 may also be defined asthe signal range in case the phenomenon to be investigated isrepresented by a signal which is processed in an attenuating amplifier,or it may be that range in which the particular phenomena ofinvestigatory interest are expected to occur. It is, furthermore,presumed that the amplitude limits defining the range 11 are selectivelyvariable within the total range 12.

Reference numeral 13 now refers to a particular analyzing band running,of course, parallel to the time axis t and being defined in any instancewithin amplitude range 11. The analyzing band 13 is selected to have avariable width, the width representing or being related to theresolution of the analyzing process. The analyzing band 13 is made toprogressively cover the range 11, i.e., range 11 is progressivelysweeped in the direction of arrow 14 or in the opposite direction 14, byprogressively shifting 13 across that amplitude range.

As the analyzing band 13 is shifted across analyzing range 1 l, forexample in incremental steps, particular events occurring within theanalyzing band are counted; for example, the number of maxima or minima,i.e., particularly directed excursion peaks of the curve 10 are counted,and the count number is associated with the particular position of theanalyzing band within the amplitude range. The position of the band maybe defined by the amplitude value of its center, and the band spreadsfor half the band width above and below that center amplitude. Thevarious counting results as resulting from different band position, areprocessed further to ascertain the desired characteristic function independence upon amplitude.

The analyzing speed, i.e., the speed of progression of analyzing band 13across the analyzing range 11, should be variable to a considerableextent and may match particular requirements in any particular case.That band 13 may progress in steps, i.e. intermittently or on acontinuous, uninterrupted basis. In case of stepwise progression ofanalyzing band 13 the amplitude equivalent of each step should be equalto the width of the band 13, or there should be a definite relationbetween step height and band width to obtain, for example, definiteoverlap. In any event, selection of width of the analyzing band andselection of the width of the steps of analyzing band progression shouldbe coupled.

Turning now to the description of FIG. la there is illustrated equipmentforcarrying out the inventive process. A measuring instrument,transducer or the like, is assumed to develop an electrical signal Urepresenting the process to be investigated and analyzed. As an inherentresult of the investigatory process or due to threshold behavior of theinstrumentation, the signal U may have amplitude not exceeding the range12.

An input circuit 1 is provided to receive signal U and to provideappropriate amplification or attenuation as well as impedance matchingfor the circuitry processing the signal U or a replica thereof. Theinput circuit 1 may include filters and particularly any do. componentsmay be removed from the signal .to restrict the analyzing process tovariable reproduced phenomina and to eliminate, for example,quasi-stationary components.

The output signal of input stage 1 is denoted K.U wherein K representsthe amplification or gain in circuit 1. In particular, the gain of unit1 as to ac. components may be below unity, so that the signal K.U,,-varies only within the range 12. The signal ICU is fed to a processingstage determining the standard deviation so that the width A U of theanalyzing band 13, as well as the amplitude differential defined by thelimits for the analyzing range 11, can be represented in units of a.

The relative position of the analyzing band as well as the progressiveshifting thereof across the analyzing range is provided by a saw toothsignal generator 3, providing a voltage U, that varies continuously orin steps. An input section 4 is provided as control stage to establishthe slope of the saw tooth wave; more generally, the rate of change ofthe output of generator 3 is established by this control stage.Accordingly, automatic or manual setting of stage 4 determines the speedof the scanning process according to which an analyzing band is shiftedacross the range of amplitudes subject to the investigation. Thatscanning and shifting speed does not have to be uniform but may varyeven during an investigatory run. The analyzing band should not becaused to dwell in any section of the amplitude range for whichsufficient information has been sampled, nor should the band scan animportant range portion at too fast a speed as the counting of eventsshould yield statistically meaningful results.

The input stage 4 determines and establishes also the range 11 to becovered by the scan, for example, in dependence upon the standarddeviation 0' This includes providing of a first signal level U and of asecond signal level U, in between which scan signal U, is caused tovary. It is assumed in particular that U, varies from U as negativeequivalent of the maximum amplitude, corresponding to the maximum limitX max as upper limit of range 11, the variation to occur toward morepositive values, to U,, corresponding to the positive equivalent of thenegative limit X min, which is the lower limit of range 11. In caseinput device 1 removes d.c. components from the information signals,analyzing range 11 should be provided to extent symmetrical to the zeroline. Thus, U =U,. This, however, is not essential in principal butmerely facilitates instrumentation and design.

The output signal U, is actually the negative equivalent of the centeramplitude of the analyzing band. A summing network 5 is provided toalgebraically add the information signal K.U,- to the scan voltage U,.The composite output signal of adder 5, K.U, U, is passed to one inputeach of two comparators 7 and 8, constructed, for example, asdifferential amplifiers, with very high gain and saturation behavior ata first level when the signal input, as derived from adder 5 exceeds therespective reference signal, and at a second level when that input isbelow the respective reference.

The second input of comparator 7 receives a reference signal A U/2 asderived from an adjustible voltage source 17, the second input ofcomparator 8 receives a reference signal A U/2 as derived from anadjustible voltage source 18. An instantaenous signal KU has valuewithin the band in case A U/2 K.U U, A U/2. Thus, the analyzing band isestablished by the range defined by U, -A U/2 and -U, A /2, and voltageA U defines the width of the analyzing band. The two adjustiblereference sources 17 and 18 are shown with interconnected adjustment.That adjustment may be controlled in response to the output by variancedetector 2.

It follows from the foregoing, that the outputs of comparators 7 and 8are dissimilar when the composite signal K.U,,- U, is larger than A U/2but smaller than A U/2. Similarity of outputs of comparators 7 and 8establishes that the information signal K.U,,- is outside of theanalyzing band. An exclusive OR gate in a logic circuit 9 may, forexample, respond to these conditions. However, different logiccombinations may lead to detection of different kinds ofcharacteristics, as will be developed more fully below.

As illustrated, the logic circuit 9 receives additional information. Forexample, a zero-crossing detector 6 responds to each polarity reversalof the information signal. It may be presumed that detector 6 is acomparator comparing signal RU U, with ground potential or zero asreference. Detector 6 provides a first signal level output when theinformation signal has positive polarity, and a second signal level whenthe information signal has negative polarity. The logic circuit 9 mayinclude various components all of which are not operating at all times.A programmer 15 is provided to establish enabling signals to severallogic gates etc. in circuit 9 to combine the inputs for the circuit soas to render the circuit responsive to the desired phenomena. Differentanalyzing programs will be explained below.

Logic circuit 9 has an output channel 91 in which appear pulses orsignals that are representative of detected specific events to which thecircuit has been rendered responsive by programmer 15. A counter 16 isconnected to receive the pulses and counts same. The counter 16 mayoperate digitally or as pulse integrator, the output of which representsthe accumulated frequency of the events observed and detected. If thecounter 16 is an integrator with fairly short time constant, the outputactually represents counted events per chosen time unit. A controlcircuit 19 is provided to control the time constant of the counter 16,for example, in dependence upon the saw tooth signal to match theintegrating-per-unit time process to the rate of change of the generator3.

As stated above, generator 3 may change output U, in steps and holdingthe respective output for a period during which counter 16 countsevents. With each step of generator 13 the counter or integrator isreset to begin counting anew.

The output signal Ui of event counter 16 may appear in digital or analogformat and is of statistical significance. Signal Ui is correlated withthe signal U, defining the amplitude center value of the band. Thesignals Ui and U, may be used as inputs for an X-Y plotter tographically record the characteristic statistical function in dependenceupon amplitude.

The method in accordance with the invention offers the opportunity toinvestigate the temporal behavior and amplitude distribution of inputsignal U,; as a function of time in accordance with six possibledistribution functions. The logic circuit 9 may include circuitry topermit all of these different analyzations to be conducted, andprogrammer 15 provides particular operationel selection so that thepulses in line 91 represent the desired phenomena.

FIG. 2 illustrates a curve 20, representing a physical quantity X as afunction of time. As time progresses, curve 20 has numerous relativemaxima 21 and minima 22. The curve 20, when represented by signal U,,-,will be processed in the circuit of FIG. 1 as follows: At the beginningof an amplitude range scan signal U, has a particular negative maximumvalue U,, so that the analyzing band is near the uppermost limit of theamplitude range to be investigated. As the processed infonnation signalKU has definitely amplitude peaks below the positive equivalent of thatlimit value, the output of summing network 5 is negative. Accordingly,the two comparators 7 and 8 provide similar outputs.

As indicated, a control connection leads from logic circuit 9 to thecontroller 4 for generator 3 providing thereto, for example, a controlsignal that causes the generator 3 to change its output at a relativelyhigh rate. Thus, the analyzing band is shifted down relatively fastuntil one or several signal peaks are encountered, which is evidenced bya change in state of comparator 8. The resulting change in input forcontroller 4 causes generator 3 to reduce the slope of the saw toothsignal U, (or to reduce the stepping rate of stepwise change in output),as now the regular operation begins.

As the signal U, increases further the analyzing band is shifted down,and relative maxima will be detected by a brief change in output ofcomparator 8 from false to true not followed by a similarly directedchange in output of comparator 7. Therefore, the logic circuit 9includes circuitry enabled by programmer for detection of relativemaxima which respond to a temporary change in output of comparator 8 notaccompanied by a change in output of comparator 7. For example,comparator 8 always changes state from false to true when the inputsignal K.U becomes larger than -U, A U/2 and this signal edge can beused to set a flip-flop 92. Comparator 7 resets the flip-flop whenchanging state upon input signal K.U exceeding the upper band limit -U,+A U/2. However, a peak when occurring in the band, will not causecomparator 7 to change state, and flip-flop 92 will remain set. If theset state of the flip-flop persists for a predetermined period of time,a maximum is recognized and a pulse is set into line 91. Operation offlip-flop 92 is restricted to change of state signals by the comparatorsin the one particular direction. For each detected maximum a pulse isthus added to the count state of counter or integrator 16.

Additionally or in the alternative relative minima 22 may be detected,counted and the counting result processed. Minima may be recognized byresponse to a change of state. of comparator 7 from true to false notaccompanied by a similarly directed change of state of comparator 8. Thelogic 9 may include circuitry responding to these situations for settingflipflop 92, or a different one, to provide pulses that are integrat'edseparately, or the minima detecting circuitry is enabled by a differentsetting of programmer 15 in which case flip-flop 92 responds to minimaonly. Detectionof maxima and minima are actually interchangeableprocesses, unless both types of extremities are to be detectedconcurrently. Thus, rather than changing the logic, the same circuitthat is used for detecting maxima, can be used for detection of minima,in that programmer 15 causes a polarity reversal of the signal U asprocessed in input circuit 1, whereby the detected maxima of theinverted curve are, of course, equivalent to the detection of minima ofthe uninverted curve. Still alternatively, the polarity of the output U,of generator 3 can be reversed or the polarity of the adding process ofnetwork 5 is reversed. In either case, the relative direction ofamplitude range scanning is reversed.

The relative maxima or the relative minima or both are regarded as therespective particular events to be counted, for example, on a per unittime basis. The counting results in a particular signal Ui representing,as statistical characteristic function, the relative frequency ofoccurrence of maxima and/or minima in curve 10 and within the respectivecurrent band centered around U,. As variable signal U, scans theamplitude range relatively slowly, gradually or in slow steps, therelative frequency of occurrence of the maxima is represented byvariations in the signal Ui, and this signal Ui is plotted againstcurrent value I of U, to obtain relative maximum/minimum frequency ofoccurrence versus amplitude characteristic.

By means of employing the inventive measuring and detection method it isalso possible to investigate a physical quantity as to frequency ofoccurrence of absolute maxima and/or minima in between two zerocrossings. FIG. 3 illustrates a function X (t) and the resultingparticular curve 30 is to be investigated so as to detect occurrence ofabsolute maxima or minima in between two zero crossing and within theanalyzing band. Such maxima are present, for example, at 31.Analogously, there are absolute minima 32. In these cases an absolutemaximum or an absolute minimum within the band represents an eventascertainment of which is to be utilized for developing a statisticalcharacteristic function.

The programmer 15, when set for detection of absolute maxima within thecurrent analyzing band, enables similar circuitry as used for detectionof relative maxima. For example, the flip-flop 92 in logic 9 is set whencomparator 8 changes state and remains set when comparator 7 does notchange state until the next zero crossing is detected by comparator 6.ln other words, the detector 6 may provide a strobing pulse that is setinto line 91 when flip-flop 92 is set at that time. Absolute minima aredetected and counted analogously.

In the foregoing, ascertainment of four different characteristicfunctions has been described on the basis of detecting maxima and/orminima as characteristic events. Aside from these methods the inventivemethod offers additional possibilities; e.g., the ascertainment ofprobability distribution and of probability distribution density, ofquantities represented as function of time and detection. FIG. 4 showsthe amplitude of a physical quantity as a function of time representedby a curve 40, and it is assumed that the probability distributiondensity is to be ascertained. For ascertaining probability distributiondensity one has to ascertain the time, i.e., the period of time in whichthe curve 40 is within the analyzing band. Ascertainment of thatcompound period per band position and proper processing of the resultleads to a function which represents probability distribution density.For this the programmer 15 may enable an exclusive or" gate 93 in logic9, providing a true output when the instantaneous value of curve 40 iswithin the band as represented by different states of comparators 7 and8. The curve is outside of the band when the comparators have similarstates. The duration of response of the exclusive or gate is counted.For this, analog type integration may be preferred although digitizationis possible.

The probability distribution itself can be ascertained throughdetermination of the relative periods for .which a curve remains below athreshold level. This is shown representatively in FIG. 5. The thresholdlevel 13' is, of course, variable, and relative periods are ascertainedduring which, for example, comparator 8 is in the state corresponding toa signal amplitude RU below the threshold as represented by signal U,AU/2. This particular acquisition process can also be generated byconsidering the operation as an asymmetric band width analysis, settingthe reference input for comparator 8 to zero, and disregarding theoutput of comparator 7, so that the band is actually defined by currentsignal level U, and lower range limit.

It was presumed in the foregoing, that amplitude signal U, is steadilyvariable, or is varied in steps of particular duration to progressivelyshift location of the analyzing band in the amplitude continuum.However, the inventive method permits stopping of the analyzing band inany particular amplitude level, so as to extend the period ofacquisition of the particular event sought to be detected. lf counter orintegrator 16 is operated to provide output or a per unit time basis,then the duration of an analyzing step at a particular amplitude levelU, is immaterial except that it should be long enough to meet therequirement of statistical observation, and that may require extensionof the observation period.

The invention is not limited to the embodiments described above but allchanges and modifications thereof not constituting departures from thespirit and scope of the invention are intended to be included.

We claim:

1. Apparatus for analyzing dynamic processes represented by a particulartime variable information signal within a range for amplitudes of thesignal comprising:

first means for providing representation of the information signal tovary within a particular amplitude range;

second means connected to the first means to superimpose thereto a timevariable signal;

third means including threshold means connected to be responsive toparticular characteristic portions of the signal to define occurrence ofthe characteristic portion of the signal within an analyzing band, andproviding logic 2. Apparatus as in claim 1, the second means providing asteadily, time variable signal in representation of amplitude rangescanning, there being means to superimpose the time variable informationsignal and the range scan signal to obtain range scanning.

3. Apparatus as in claim 1, the second means providing a step functionsignal in representation of stepwise amplitude range scanning, therebeing means to superimpose the time variable information signal and therange scan signal to obtain range scanning.

4. Apparatus as in claim 2, the width of the band as provided by thethird means, being particularly related to the value of amplitudeincrement for each step.

5. Apparatus as in claim 1, the second means providing an amplitude scansignal variable between first and second limits defining the amplitudeanalyzing range, the value of the scan signal defining the position ofthe analyzing band within the amplitude range.

6. Apparatus as in claim 5, at least one of the first and second limitsbeing adjustable.

7. Apparatus as in claim 5, including means to reverse the relationshipbetween scan direction and polarity of the information signal.

8. Apparatus as in claim 1, including means for adjusting the rate ofshifting as provided by the fourth means.

9. Apparatus as in claim 1, including means for maintaining theanalyzing band at a particular amplitude within the range.

10. Apparatus as in claim 1, and including means operating the secondmeans for providing relative fast shifting of the analyzing band untilthe third means has detected at least one said characteristic portions,and operating the fourth means subsequently for a slower rate ofshifting.

11. Apparatus as in claim 1, the third means responsive to relativemaxima of the information signal as the characteristic portion.

12. Apparatus as in claim 1, and including means connected to beresponsive to zero crossings of the information signal, the third meansresponsive to maxima of the information signal and to the detected zerocrossings for detection of absolute maxima in between zero crossings asthe characteristic portion.

13. Apparatus as in claim 1, the third means responsive to relativeminima of the information signal as the characteristic portion.

14. Apparatus as in claim 1, and including means connected to beresponsive to zero crossings of the information signal, the third meansresponsive to minima of the information signal and to the detected zerocrossings for detection of absolute minima in between zero crossings asthe characteristic portion.

15. Apparatus as in claim 1, the third means responsive to persistanceof information of information amplitudes in the analyzing band.

16. Apparatus as in claim 1, the third means responsive to signalamplitudes different from signal levels of at least one limit as definedby the band.

1. Apparatus for analyzing dynamic processes represented by a particulartime variable information signal within a range for amplitudes of thesignal comprising: first means for providing representation of theinformation signal to vary within a particular amplitude range; secondmeans connected to the first means to superimpose thereto a timevariable signal; third means including threshold means connected to beresponsive to particular characteristic portions of the signal to defineoccurrence of the characteristic portion of the signal within ananalyzing band, and providing logic signals representative of suchoccurrence; fourth means connected to the second and third means toprovide variable representation corresponding to shifting the analyzingband within the amplitude range for the signal; and fifth meansconnected to the third means to accumulate the logic signals asstatistical representation evaluation of the occurrence of thecharacteristic portions in dependence upon amplitude as represented bythe amplitude variable representation of position of the analyzing bandwithin the amplitude range.
 2. Apparatus as in claim 1, the second meansproviding a steadily, time variable signal in representation ofamplitude range scanning, there being means to superimpose the timevariable information signal and the range scan signal to obtain rangescanning.
 3. Apparatus as in claim 1, the second means providing a stepfunction signal in representation of stepwise amplitude range scanning,there being means to superimpose the time variable information signaland the range scan signal to obtain range scanning.
 4. ApParatus as inclaim 2, the width of the band as provided by the third means, beingparticularly related to the value of amplitude increment for each step.5. Apparatus as in claim 1, the second means providing an amplitude scansignal variable between first and second limits defining the amplitudeanalyzing range, the value of the scan signal defining the position ofthe analyzing band within the amplitude range.
 6. Apparatus as in claim5, at least one of the first and second limits being adjustable. 7.Apparatus as in claim 5, including means to reverse the relationshipbetween scan direction and polarity of the information signal. 8.Apparatus as in claim 1, including means for adjusting the rate ofshifting as provided by the fourth means.
 9. Apparatus as in claim 1,including means for maintaining the analyzing band at a particularamplitude within the range.
 10. Apparatus as in claim 1, and includingmeans operating the second means for providing relative fast shifting ofthe analyzing band until the third means has detected at least one saidcharacteristic portions, and operating the fourth means subsequently fora slower rate of shifting.
 11. Apparatus as in claim 1, the third meansresponsive to relative maxima of the information signal as thecharacteristic portion.
 12. Apparatus as in claim 1, and including meansconnected to be responsive to zero crossings of the information signal,the third means responsive to maxima of the information signal and tothe detected zero crossings for detection of absolute maxima in betweenzero crossings as the characteristic portion.
 13. Apparatus as in claim1, the third means responsive to relative minima of the informationsignal as the characteristic portion.
 14. Apparatus as in claim 1, andincluding means connected to be responsive to zero crossings of theinformation signal, the third means responsive to minima of theinformation signal and to the detected zero crossings for detection ofabsolute minima in between zero crossings as the characteristic portion.15. Apparatus as in claim 1, the third means responsive to persistanceof information of information amplitudes in the analyzing band. 16.Apparatus as in claim 1, the third means responsive to signal amplitudesdifferent from signal levels of at least one limit as defined by theband.